1. Field of the Invention
The present invention relates to an optical switch for use in change-over between optical paths in an optical communication facility.
2. Description of the Background Art
Referring to FIG. 12, description will be given of a prior art optical switch 100. Optical switch 100 is one shown in TuM1 (reported by J. E. Fouquet, entitled xe2x80x9cCompact Optical Cross-Connect Switch Based on Total Internal Refection in a Fluid-Containing Planar Lightwave Circuitxe2x80x9d) in OFC 2000 (Optical Fiber Communication Conference, Mar. 7, 2000). Optical switch 100 is constituted of a silica planar optical circuit substrate 51 and square optical waveguides each with a slightly higher refractive index are formed in silica planar optical circuit substrate 51, thereby forming a two-dimensional optical circuit.
Generally speaking, silica planar optical circuit substrate 51 in use is of a refractive index of the order of 1.5 and an optical waveguide 2 is made of a material with a refractive index higher by a value of the order of 1% than that of substrate 51. A portion of optical waveguide 2 is usually called a core as well. A trench 52 is formed so as to traverse optical waveguides 2 at a cross-point thereof where both partly overlap, and filled with a refractive index matching oil 56. Refractive index matching oil 56 has a refractive index equal to that of optical waveguide 2.
Description will be given of operation of optical switch 100. Optical switch 100 has a bubble generation mechanism not shown, which can generate or thereafter again make extinct a bubble 53 within refractive index matching oil 56 at the cross-point of optical waveguides 2. The bubble generation mechanism can adopt a mechanism similar to that for use in a bubble jet (R) printer head.
When generated bubble 53 is present at a cross-point, all the energy of incident light on the cross-point is reflected by a surface of bubble 53, while contrary to this, when no bubble 53 is present there, light propagates straight through the cross-point since optical waveguide 2 and refractive index matching oil 56 have the same refractive index as each other. By utilizing this nature associated with generation and extinction of bubble 53, optical paths can be changed over between two states of reflection and straight propagation, respectively.
In optical switch 100 constructed as described above, a width of trench 52 was required to be at least a value of the order of 15 xcexcm in consideration of precision in etching process. Furthermore, there was a problem that an optical loss of at least 0.07 dB per cross-point arises. All the optical loss L in optical switch 100 is given by the following formula:
L=2C+(mxe2x88x921)T+(nxe2x88x921)T+R
where m is the number of input ports, n is the number of output ports, C is a combined loss occurring when light is launched into an optical switch from an optical fiber and thereafter, in passage through an optical waveguide till an active region, which is at a cross-point, T is a loss [dB] occurring in the course where light traverses one trench and propagates across a section of a short optical waveguide between two adjacent cross-points, and R is a loss caused by reflections at sidewalls in an empty trench and propagation across a section of a short optical waveguide between two adjacent cross-points.
For example, in a case where an optical switch on as large a scale as a 1000 times 1000 array is desired to be constructed, all the optical loss, when detailed data is substituted into the formula, is given as follows:
L=2xc3x970.25+(1000xe2x88x921)xc3x970.07+(1000xe2x88x921)xc3x970.07+2.1=142.46 dB
Therefore, all the optical loss of 142.46 dB still occurs even in a case where the optical switch is fabricated in ideal conditions. In order to cause an optical switch to normally function as such without degrading a signal quality, a necessity is to restrict the optical loss to 10 dB or lower. When considering such an optical loss, there was a problem of difficulty in fabricating an optical switch on a scale larger than of the order of a 32 times 32 array if such a construction is adopted.
Worse yet, since silica planar optical circuit substrate 51 is fabricated using apparatuses similar to those for use in a case of a semiconductor device, a problem was present that a large size optical switch required a very high cost. In addition, since bubble 53 is utilized that is generated each time within refractive index matching oil 56 it becomes necessary, a problem arose that bubble 53 generated was small or shifted out of place to thereby generate optical path change-over abnormality. Moreover, a problem was present since a local light absorption occurs in small particles of refractive index matching oil 56 according to a state of refractive index matching oil 56, with the result that a peripheral region around an optical path is burned by the energy of signal light.
Furthermore, since a prior art optical switch has a physical limitation on compactness, there has been a request for an optical switch of a construction capable of downsizing itself.
It is an object of the present invention to provide an optical switch capable of reducing an optical loss without generating the change-over abnormality or the burning described above. It is another object of the present invention to provide an optical switch capable of further downsizing itself.
An optical switch of the present invention includes: a plate member, constituted of an elastic material, and having first and second optical waveguides intersecting with each other at a cross-point in the interior thereof and a cut formed so as to traverse the cross-point; and press means, provided on at least one of upper and lower sides of main surfaces of the plate member, and pressing the cut to open or close the cut, wherein when the cut is open, light propagating through the first optical waveguide is reflected by an inner wall surface of the cut to then, propagate through the second optical waveguide, while when the cut is close, light passes through the cut to keep on propagating straight through the first optical waveguide and the press means is formed from an piezoelectric member that deforms according to an pizoelectric effect.
According to the above construction, not only can an optical loss be reduced, but also change-over abnormality and burning can be prevented from occurring. Furthermore, since the press means is made from a piezoelectric material deformed by a piezoelectric effect, the optical switch can be downsized.
An optical switch of the present invention more preferably has the piezoelectric member including: a fixed part fixed to the plate member; and a moving part not fixed to the plate member, wherein a position of the moving part changes upward or downward relative to the fixed part by a piezoelectric effect, such that the moving part presses the cut. With such a construction adopted, the fixed part is fixed to the plate member to thereby enable a press force required with certainty to be given to a cut, since a position of the piezoelectric member relative to the plate member is the same at all times even if a flatness of the plate member is not kept.
An optical switch of the present invention has the press means constituted of a piezoelectric sheet having fixed parts and moving parts, wherein each of the moving parts may be formed using one of portions formed by isolation cuts each of which is separation created by cutting of the piezoelectric sheet to extend to the depth of thickness from the front side to the backside, while the piezoelectric sheet is still in one body in great part thereof. With such a construction adopted, since the moving parts and the fixed parts can be formed only by isolation cuts therein, thus facilitating fabrication of press means.
An optical switch of the present invention may have the piezoelectric sheet in which isolation cuts are formed to each form a comb-shaped configuration and by use of each tooth portion of each comb-shaped configuration, one of moving parts are formed. According to such a construction, plural piezoelectric members can be formed with good efficiency.
An optical switch of the present invention may have moving parts thereof formed by use of respective portions of the piezoelectric sheet each between two adjacent straight isolation cuts of a pair in parallel of plural straight isolation cuts formed in the piezoelectric sheet. According to such a construction, plural piezoelectric members can be formed with good efficiency.
An optical switch of the present invention has a piezoelectric member, which is a member of a flat plate, and only a requirement for which is that the flat plate is restrained from moving out from a peripheral end surface thereof. With such a construction adopted, since a piezoelectric member constituted of a flat plate member as a whole can deform the plate member, the plate member can be deformed such that opening/closing of a cut can be achieved without giving irreversible plastic deformation to the plate member.
It is more preferable that an optical switch of the present invention has piezoelectric members provided on the upper side and lower side of the plate member. According to this construction, at least one of the upper and lower sides of the plate member is selected and deformation can be generated on the selected one side, thereby enabling opening/closing a cut can be achieved with good efficiency.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.